Scientists have created a human-pig hybrid in a milestone study that raises the prospect of being able to grow human organs inside animals for use in transplants.
It marks the first time that embryos combining two large, distantly-related species have been produced. The creation of this so-called chimera–named after the cross-species beast of Greek mythology–has been hailed as a significant first step towards generating human hearts, livers and kidneys from scratch.
Juan Carlos Izpisua Belmonte, who led the work on the part-pig, part-human embryos at the Salk Institute for Biological Studies in La Jolla, California, said: “The ultimate goal is to grow functional and transplantable tissue or organs, but we are far away from that. This is an important first step.”
The study has reignited ethical concerns that have threatened to overshadow the field’s clinical promise. The work inevitably raises the spectre of intelligent animals with humanised brains and also the potential for bizarre hybrid creatures to be accidentally released into the wild. The US National Institutes of Health (NIH) placed a moratorium on funding for the controversial experiments last year while these risks were considered.
Izpisua Belmonte said that fears around chimeras were inspired largely by mythology rather than the realities of meticulously controlled experiments. But he acknowledged: “The idea of having an animal being born composing of human cells creates some feelings that need to be addressed.”
Professor Daniel Garry, a cardiologist and head of a different chimera project at the University of Minnesota, said that the rapid progress in chimera research had prompted a range of troubling questions, including whether the progeny would look more human or more pig, what would happen if a chimera had a human thought and whether it was possible for the human cells to cannibalise the pig embryo, resulting in a mostly-human, slightly-pig offspring.
